The present invention relates to a process for dipping a ply of greige cords, used for reinforcing pneumatic tires, and pneumatic tires comprising radial carcass plies made with such cords.
Radial carcass tires, having a reinforcing member disposed radially outwardly of the belt assembly and comprising textile cords oriented at small angles with respect to the mid-circumferential plane of the tire, have been found to be particularly durable when subjected to high revolution speeds.
Such a reinforcing member, referred to as an overlay ply, may comprise a spirally wound strip, made from cord reinforced elastomeric material, located radially outward of the belt plies. Generally, the material of the reinforcing cords have a low modulus, for instance nylon, in order to accommodate the expansion of the belt during the shaping and vulcanizing steps in the manufacture of a tire. The modulus of a cord is, inter alia, a function of the twist of the different yarns used in the cord, the cord twist, and the manner that the cord is subjected to the dipping operation.
High modulus materials, e.g. aramid, have potential advantages in high speed tires in view of their dimensional stability, but because of their dimensional stability, such cords must be twisted, so that the finished cord has the expansion potential required to match the expansion that a tire goes through during shaping and vulcanizing.
EP-A-412 928 discloses a textile overlay structure which is reinforced with cords made of aramid; the cords have a twist multiplier (as defined herebelow) between 6 and 14 and at least one of the yarns included in the cords has a twist of at least 14 turns per inch (TPI) (540 turns per meter (TPM)). Tires comprising such an overlay structure, however, have an increased noise emission, because the high modulus aramid cords vibrate like violin strings in the tire.
It is an object of the present invention to provide a process for coating a ply of greige cords, used for reinforcing pneumatic tires, with an adhesive, without substantially changing the physical properties of the cords.
It is a further object of the present invention to provide a pneumatic tire with an overlay structure reinforced with aramid cords, which has a low gauge, low noise emission, and maintains good high speed properties.
Other objects of the invention will be apparent from the following description and claims.